This invention relates to a pattern recognition device and to a method of recognizing hand-drawn patterns, created with a computer digitizing mechanism, by tracking and classifying the angular motion of the mechanism in creating the patterns.
Known pattern recognition devices can store in computer memory, and operate on, a set of coordinate points that represent a hand-drawn "artifact." The artifact is an arbitrarily-drawn shape or stroke which signifies a letter, number, or other symbol which, in turn, can represent a command sequence or operation to be performed by the computer. The shape or stroke is represented by a series of coordinate points.
According to some prior art techniques, the coordinate points of a shape or stroke are classified into three groups, each of which incorporates a set of consecutive points. The first group, line segments, include those cases where the slope between a given subset of consecutive points and the line formed by the endpoints of the line segment does not exceed a pre-determined value. The second group, arcs, include those cases where that slope does exceed a pre-determined value; the third group includes those cases where it is ambiguous as to whether the set of points forms a line segment or an arc. The digitized coordinate points are then compared to a plurality of previously-recorded and similarly-represented patterns. Recognition is achieved by determination of the match of greatest similarity between the classification of the digitized points and previously defined patterns.
One problem with these prior art techniques is that the digitized sets of coordinate points are stored in their entirety before the representations of line segments, arcs, and cases where such a determination is ambiguous, are computed. This can require a significant amount of computer storage and increase the time needed for the comparison operation. Another problem with these prior art techniques can arise if no smoothing of the data occurs. Because the digitized set of coordinate points results from human hand motion, the exact set of coordinate points received and its subsequent classification can vary greatly with successive attempts to create the same pattern, even by the same individual. This can lead to poor success in correctly recognizing a hand-drawn pattern.